As industries have diversified and advanced in recent years, electronic devices such as audio-visual devices and personal computers have been dramatically reduced in size and weight, increased in memory capacity, and increased in information processing speed. Such electronic devices employ various rotating devices, for example, rotating devices for driving magnetic disks and optical discs such as FD, MO, zip, mini disc, compact disc (CD), DVD and hard disk. The reduction in size and weight and the increase in memory capacity and information processing speed of these electronic devices are greatly attributed to improvement in bearings, which are essential to the rotating devices. In particular, a fluid bearing, which is made up of a sleeve and a shaft facing each other via a lubricant, is not only suitable for reducing size and weight of electronic devices but also is highly silent and economical, because it does not have a ball bearing. Because of these characteristics, the fluid bearing has been increasingly used in personal computers, audio devices, visual devices, car navigation systems and the like.
There have been proposed lubricants and bearing fluids for use in the fluid bearing. Examples of such lubricants and fluids include: olefinic synthetic oils, diester synthetic oils and neopentyl polyol ester synthetic oils; those made from grease which contains (i) one selected from squalane and naphthenic mineral oils or a combination of any of these oils as a base oil and (ii) a urea compound as a consistency increasing agent (thickener) (refer to Patent Literature 1); those containing (i) a fatty acid triester, which is obtained from trimethylolpropane, as a base oil and (ii) a hindered phenol antioxidant and a benzotriazole derivative (refer to Patent Literature 2); those containing, as a base oil, a specific monocarboxylate ester having a phenyl group and/or a specific dicarboxylate ester (refer to Patent Literature 3); those containing a single-component composition as a base oil (refer to Patent Literature 4); those containing (i) a carbonate ester compound as a main component of a base oil and (ii) a sulfur-containing phenolic antioxidant and zinc extreme-pressure agent (refer to Patent Literature 5); those containing (i) a mixture containing a specific saturated alkyl carbonate ester as a base oil and (ii) a phenolic antioxidant (refer to Patent Literature 6); and those containing (i) a specific dialkyl carbonate ester as a base oil solvent and (ii) magnetic particles dispersed in the base oil solvent (refer to Patent Literature 7).